74 



EIGHTH REPORT — 1838. 



Table XIV. 



If we combine these twenty-four results by the method of 

 least squares, we obtain the following values : .r= + "2658 

 ^=-•5270; z<=-63° 14'; r = 0'-590 ; and S =70° 50'-l on 

 the 1st of August, 1837j at the mean geographical position of 

 which the Latitude is 53" 49', and the Longitude 2° 08'. 



Captain Ross's Observations. — In this extensive series no less 

 than fifteen needles were employed. Those designated as R L 1 

 and R L 2, J, C, C 2, and C 3, were four-inch needles made by 

 Robinson, and used in a circle made by Jones ; the remainder 

 R L 3, R L 4, R 3, R 4, R 5, R 6, R 7, W 1, and W 2, were six- 

 inch needles, also by Robinson, and used in a circle by the same 

 artist : R 4, R 5, R 6, R 7, W 1, and W 2, were fitted with revol- 

 ving axles, and were found on trial to give accordant dips in 

 dififerent positions of the axle : each observation with them re- 

 corded in the following tables is a mean of the usual eight 

 positions. For these needles, consequently, no corrections 

 are applied, and it will be seen by the observations at West- 

 bourne Green in June, July, and December, 1838, that all 

 these needles gave very nearly the same dip when used under 

 like circumstances of time and place. Their mean result at 

 Westbourne Green has been employed by Captain Ross as a 

 standard to furnish corrections for the other needles which he 

 had employed previously, and on which he could not rely with 

 equal confidence. Of these, RL 1, R L 2, R L 3, and R L 4, were 

 used for the intensity as well as for the dip, and their poles, 

 therefore, were not reversed. They were always used in pairs, 

 and the correction determined for the mean result of R L 1 and 

 R L 2 was + 3, and that for R L 3 and R L 4, + 1 6. 



